This application is based on application No. JP2001-221333 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a multi-degree-of-freedom drive mechanism which is improved. More concretely, the invention relates to the multi-degree-of-freedom drive mechanism which is improved by using an electro-mechanical transducer.
2. Description of the Related Art
There suggests an actuator in which one end of a drive shaft is fixed and an electro-mechanical transducer is connected to the other end, a lengthwise resonance is generated in the drive shaft by the electro-mechanical transducer, and a slider spring-jointed to the drive shaft is driven along the drive shaft. Since this kind of actuator is fixed at an opposite side to the electro-mechanical transducer, the fixed section can be strengthen, and the actuator is suitable to the case where a plurality of actuators are combined so as to compose a multi-degree-of-freedom drive mechanism. For example, when one end of the drive shaft of a second actuator is fixed to a slider of a first actuator, a slider of the second actuator can be driven with two degrees of freedom by electro-mechanical transducers of the first and second actuators.
However, when the same type of actuators are connected to be used, a malfunction, such that oscillation which is generated by driving one actuator is transmitted to the other actuator and although an electro-mechanical transducer of the other actuator is not driven, a slider of the other actuator moves, occasionally occurs.
In order to prevent such a malfunction, there considers a method of inserting a shock absorbing member between the slider and the drive shaft when the actuators are connected. However, when the shock absorbing member is inserted, the structure becomes complicated, and this causes a deterioration of rigidity and increases of the cost of parts and assembly cost in a whole drive mechanism.
The present invention is devised in order to solve the above problem, and its object is to provide a multi-degree-of-freedom drive mechanism which is improved. More concretely, it is an object of the present invention to provide a multi-degree-of-freedom drive mechanism which is improved by using an electro-mechanical transducer. More concretely, it is an object of the present invention to provide a multi-degree-of-freedom drive mechanism which is capable of preventing a malfunction with a simple structure.
In order to achieve the above object and another objects, a multi-degree-of-freedom drive mechanism according to one aspect of the present invention includes at least two first and second actuators which have: an electro-mechanical transducer; a drive shaft to which the electro-mechanical transducer is fixed at its one end; and a driven member which is frictionally engaged with the drive shaft, and which generate lengthwise resonance in the drive shaft by means of the electro-mechanical transducer so as to be capable of moving the driven member along the drive shaft, wherein the other end of the drive shaft of the second actuator is fixed to the driven member of the first actuator directly or via another actuator, and the first and second actuators are composed so that resonating frequencies of the respective drive shafts are different from each other.
In the above structure, when the actuator suitably drives the electro-mechanical transducer with a drive frequency at which lengthwise resonance is generated in the drive shaft, the drive shaft oscillates at different speeds according to expansion and contraction, for example, and the driven member which is frictionally engaged with the drive shaft moves along the drive shaft. The electro-mechanical transducer is an element, such as a piezoelectric element, magnetostrictive element, electrostrictive element or electrostatic actuator, which can transduce an electric energy (for example, voltage, electric current, electric field, electric charge, static electricity, magnetic field, etc.) into a mechanical energy (for example, deformation and distortion such as expansion and contraction, dilatation, curving, or twisting).
According to the above structure, when the resonating frequencies of the first and second actuators are made to be suitably different and one actuator is driven, oscillation is not generated in the drive shaft of the other actuator due to oscillation of one actuator, so that a malfunction can be prevented. In order to make the resonating frequencies different, for example, length, density, elastic modules and damping coefficient are made to be different between the drive shafts, or the masses are made to be different between the electro-mechanical transducers. Namely, the structures of the actuators do not have the same structure, and thus a special member such as a shock absorbing member is not required.
Therefore, a malfunction can be prevented by the simple structure.
In the multi-degree-of-freedom drive mechanism according to another aspect of the present invention, the respective actuators drive the electro-mechanical transducers with drive frequencies included in the resonating frequencies of the drive shafts or resonating frequencies bands in the vicinity of the resonating frequencies, respectively, and the drive frequency of the first actuator is out of the resonating frequency band of the second actuator including the drive frequency of the second actuator, and the drive frequency of the second actuator is out of the resonating frequency band of the first actuator including the drive frequency of the first actuator.
As for the drive frequencies of the actuators, the resonating points with degrees where resonance of the drive shafts becomes as large as possible are selected and the drive frequencies are set at the resonating points or their vicinities, so that the actuators can be driven efficiently. However, in this case, an actuator is easily resonated due to the oscillation of another actuator. With the above structure, since the drive frequencies of the actuators do not close to each other, when one actuator is driven, the other actuator can be prevented from malfunctioning.
In the multi-degree-of-freedom drive mechanism according to another aspect of the present invention, the drive frequency with which the first actuator is driven is out of the resonating frequency band of the second actuator with a different degree from that of the above resonating frequency band of the second actuator including the above drive frequency of the second actuator, and the drive frequency with which the second actuator is driven is out of the resonating frequency band of the first actuator with a different degree from that of the above resonating frequency band of the first actuator including the above drive frequency of the first actuator.
Even if the drive frequency of one actuator is not included in the resonating frequency band including the drive frequency of the other actuator, when it is included in the resonating frequency band with another degree of the other actuator, the other actuator occasionally malfunctions. With the above structure, since the drive frequency of an actuator is not included in a resonating frequency band with another degree, a malfunction can be prevented more securely.
In the above structures, the resonating frequency bandwidth can be determined suitable per degree.
Moreover, in the multi-degree-of-freedom drive mechanism according to another aspect, the respective resonating frequency bands include frequencies in the vicinity of the resonating frequencies where an amplitude not less than 1/{square root over (2)} times as large as the maximum amplitude in the resonating frequencies is given to the drive shafts of the actuators.
In the above structure, the amplitude becomes not less than 1/{square root over (2)} times as large as the maximum amplitude in the resonating frequency bands, and an oscillation energy becomes not less than half of that at the resonating point. With the above structure, the resonating frequency bandwidth can be set to be narrow when the resonance is sharp and to be wide when the resonance is not sharp. Therefore, the resonating frequency bandwidth can be set quantitatively and reasonably according to the sharpness of the resonance.